The use of electrographic processes to form electrostatic images is well known in the art. In such processes, a latent image, in the form of applied electric charges, is produced directly on a substrate having a dielectric surface using an electrostatic printer. The printer operates by depositing charges imagewise onto the dielectric surface of the substrate using a scanning stylus or a plurality of styli arranged in linear arrays across the width of the dielectric surface to create the desired imagewise charge patterns. The substrate with the latent image applied is then passed through a toning station where an appropriately charged toner is applied to the oppositely charged surface of the substrate to produce a toned image. The toning station may include a fixing substation where the applied toner is fixed by heat or pressure or both. Color images may be generated using a plurality of serially positioned charge depositing and/or toning stations which operate sequentially to apply, for example, three or four colors to generate a colored image.
A problem for the electrographic printing industry is that there are many substrates upon which it is desirable to print. Many of these can conceivably be manufactured in forms suitable for direct electrographic imaging but their development or manufacture is uneconomical and hence they are either expensive or they are unavailable. Other substrates include those which because of their physical properties (including bulk, stiffness, low strength, elasticity, or structure) cannot be transported through an electrostatic printer and hence are completely unsuited for electrographic imaging. Thick films, papers and boards, as well as wooden, ceramic and metal surfaces are but a few examples. The ability to provide images on such substrates is desirable.
Electrographic processes for forming images on many of the above-discussed substrates which cannot be transported through a printer are known. These processes typically involve transfer of an electrostatically formed and developed image from an electrographic transfer sheet to a final substrate using polyvinyl chloride (PVC) film as an intermediate transfer medium. The electrostatically formed and developed image is formed on an electrographic transfer sheet and then transferred to the PVC film. The PVC film, with the electrostatically formed and developed image adhered to it, is then adhered to the final substrate. The PVC film that is typically used with these processes is either a calendered or dispersion cast monolayer PVC film. While the use of these PVC films has met with success in the marketplace, the PVC films have also been found to be not entirely acceptable. Neither the PVC films, nor the processes used for making such films, are environmentally friendly. The present invention, which employs the use of a unique multilayered receptor laminate that does not contain PVC, overcomes these problems.
U.S. Pat. No. 4,946,532 discloses composite facestocks and liners made of multilayer polymeric films. The multilayer film is comprised of a coextrudate containing core or base layer and skin layers overlying each side of the core layer. The core layer contains a filler material.
U.S. Pat. No. 5,106,710 discloses an electrographic process for producing a multicolored toned image in an electrostatic printer. The process disclosed therein includes the steps of: a) providing a flexible imaging sheet having a surface exhibiting dielectric properties and toner release properties; b) moving the imaging sheet through the printer; c) producing on the surface of the imaging sheet an electrostatic latent image corresponding to a desired color by imagewise deposition of charges; d) developing the latent image with a toner to form a toned image; e) drying the toned image; f) repeating steps c), d), and e) in sequence using toners corresponding to other colors to complete the multicolored toned image; and g) bringing the multicolored toned image formed on the imaging sheet in contact with a receptor sheet under pressure and at an elevated temperature, so that said image is transferred to the receptor sheet. The receptor sheet surface has a surface energy greater than the surface energy of the imaging sheet surface, and has a glass transition temperature between 10.degree. C. and 105.degree. C. The receptor sheet is comprised of a polymer selected from the group consisting of acrylics, polyolefins, polyvinyl acetals, PVC and polyurethane film.
U.S. Pat. No. 5,435,963 discloses an oriented polymeric in-mold label film that includes a hot-stretched, annealed, linerless self-wound film lamina. The film is disclosed as having a face layer for printing, a central layer, and a base layer which includes a heat-activatable adhesive. The working examples disclose a label film with the face layer disclosed as being a mixture of an ethylene/vinyl acetate copolymer and a polypropylene homopolymer. The central layer is disclosed as being a mixture of an ethylene/vinyl acetate copolymer, either polypropylene homopolymer or a random polypropylene copolymer, and optionally a titanium dioxide concentrate. The base layer is disclosed as being a mixture of an ethylene/vinyl acetate copolymer, either a polypropylene homopolymer or a low density polyethylene, and optionally a heat-activatable adhesive and an antistat.
U.S. Pat. No. 5,601,959 discloses a process and associated element for forming an image on a substrate using an electrographic element comprising a releasable dielectric image receptive layer supported on an electrically conductive carrier sheet by applying an adhesive coating on the substrate front surface, producing a toned image on the image receptive dielectric layer, contacting the image to the adhesive layer thereby adhering the electrographic element to the substrate, and separating and removing the carrier sheet from the image receptive layer, whereby the image receptive layer and the toned image remain on the substrate.